HR: 1400h
AN: G43B-07    [Abstracts]
TI: Block Modeling of Crustal Deformation in the Northern Walker Lane, Western Basin and Range, to Improve Estimates of Seismic Hazard
AU: * Hammond, W C
EM: whammond@unr.edu
AF: Nevada Bureau of Mines and Geology and Nevada Seismological Laboratory, University of Nevada, Reno, Reno, NV 89557-0178, United States
AU: Kreemer, C
EM: kreemer@unr.edu
AF: Nevada Bureau of Mines and Geology and Nevada Seismological Laboratory, University of Nevada, Reno, Reno, NV 89557-0178, United States
AU: Blewitt, G
EM: gblewitt@unr.edu
AF: Nevada Bureau of Mines and Geology and Nevada Seismological Laboratory, University of Nevada, Reno, Reno, NV 89557-0178, United States
AB: In the United States, seismic hazard is evaluated officially by the U.S. Geological Survey and published as estimates in the National Seismic Hazard Maps (NSHM) that depict the peak ground shaking at a specific level of likelihood. In the western Great Basin, the 2002 NSHM is based on a combination of seismic, geologic and geodetic data. However, a discrepancy between the deformation rate that is inferred from the geodetic data (e.g. GPS) and geologic data (e.g. slip rates from fault studies) led to the introduction of an ad hoc zone of crustal shear strain in the western Basin and Range. Only then was the shaking risk portrayed in the NSHM consistent with the relative geodetic velocity of the Sierra Nevada microplate with respect to the central Great Basin. Since creation of the 2002 NSHM there has been a rapid increase in the quantity, quality and spatial coverage of GPS data in the western Great Basin, providing a vast improvement on the constraint on the pattern of crustal deformation. Thus geodesy is poised to make a substantial contribution to the spatial localization of seismic hazard in support of the next generation NSHM. In the Walker Lane ~10 mm/yr of relative motion are accommodated as shear and extension along a ~200 km wide and ~1000 km long zone of intracontinental deformation associated with the Pacific/North American plate boundary. We integrate GPS velocities obtained from sites in the continuous BARGEN, PBO, BARD, semi-continuous MAGNET network plus campaign results from numerous published results to constrain block models of crustal deformation. In so doing we estimate slip rates on block-bounding faults that have regional kinematic self-consistency and can be easily incorporated into the USGS algorithms that compute estimates for seismic hazard. Because of the large number and high density of candidate faults, and length of this zone we divide the region into three parts covering the Northern, Central and Southern Walker Lane. We have completed building the models for the northern Walker Lane (latitude 38.5 to 40.5 degrees, longitude - 120 to -117 degrees) and will present results from this section. The model has 62 blocks with mean dimension of ~30 km on a side, and thus the blocks are small compared to the width of the expected signal owing to elastic strain accumulation across locked faults. This starting number of blocks is purposefully large. We will discuss the ability that the data have to resolve details in the pattern of crustal deformation, and make a special effort to quantify the uncertainties and trade-offs in slip rates of nearby faults whose strain signals can overlap.
DE: 0468 Natural hazards
DE: 1209 Tectonic deformation (6924)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Geodesy [G]
MN: 2007 Joint Assembly